fix crash in view culling when parent-child go from flattened-unflattened to unflattened-flattened (facebook#50844)

Summary:
Pull Request resolved: facebook#50844

changelog: [internal]

Fixes a problem where during reparenting differentiator will generate invalid mounting instructions. In tests, this fails with assertion failure on [StubViewTree.cpp:177](https://github.com/facebook/react-native/blob/main/packages/react-native/ReactCommon/react/renderer/mounting/stubs/StubViewTree.cpp#L177).

Reviewed By: rubennorte

Differential Revision: D72822113

fbshipit-source-id: 924fca76a87119c3a86c19dc974f4ec282b149d5

Author: sammy-SC

packages/react-native/Libraries/Components/ScrollView/__tests__/ScrollView-viewCulling-itest.js

@@ -9,6 +9,7 @@
  * @oncall react_native
  * @fantom_flags enableViewCulling:true
  * @fantom_flags enableSynchronousStateUpdates:true
+ * @fantom_flags enableFixForParentTagDuringReparenting:true
  */
 
 import 'react-native/Libraries/Core/InitializeCore.js';
@@ -1239,3 +1240,78 @@ test('parent-child flattening with culling', () => {
     'Insert {type: "View", parentNativeID: (N/A), index: 0, nativeID: "child"}',
   ]);
 });
+
+test('parent-child switching from unflattened-flattened to flattened-unflattened', () => {
+  const root = Fantom.createRoot({viewportWidth: 100, viewportHeight: 100});
+
+  Fantom.runTask(() => {
+    root.render(
+      <ScrollView
+        style={{height: 100, width: 100}}
+        contentOffset={{x: 0, y: 60}}>
+        <View
+          style={{
+            marginTop: 100,
+            opacity: 0,
+          }}>
+          <View
+            style={{
+              marginTop: 50,
+            }}>
+            <View
+              nativeID={'child'}
+              style={{height: 10, width: 10, backgroundColor: 'red'}}
+            />
+          </View>
+        </View>
+      </ScrollView>,
+    );
+  });
+
+  expect(root.takeMountingManagerLogs()).toEqual([
+    'Update {type: "RootView", nativeID: (root)}',
+    'Create {type: "ScrollView", nativeID: (N/A)}',
+    'Create {type: "View", nativeID: (N/A)}',
+    'Create {type: "View", nativeID: (N/A)}',
+    'Create {type: "View", nativeID: "child"}',
+    'Insert {type: "View", parentNativeID: (N/A), index: 0, nativeID: "child"}',
+    'Insert {type: "View", parentNativeID: (N/A), index: 0, nativeID: (N/A)}',
+    'Insert {type: "View", parentNativeID: (N/A), index: 0, nativeID: (N/A)}',
+    'Insert {type: "ScrollView", parentNativeID: (root), index: 0, nativeID: (N/A)}',
+  ]);
+
+  // force view to be flattened.
+  Fantom.runTask(() => {
+    root.render(
+      <ScrollView
+        style={{height: 100, width: 100}}
+        contentOffset={{x: 0, y: 60}}>
+        <View
+          style={{
+            marginTop: 100,
+          }}>
+          <View
+            style={{
+              marginTop: 50,
+              opacity: 0,
+            }}>
+            <View
+              nativeID={'child'}
+              style={{height: 10, width: 10, backgroundColor: 'red'}}
+            />
+          </View>
+        </View>
+      </ScrollView>,
+    );
+  });
+
+  expect(root.takeMountingManagerLogs()).toEqual([
+    'Update {type: "View", nativeID: "child"}',
+    'Remove {type: "View", parentNativeID: (N/A), index: 0, nativeID: "child"}',
+    'Remove {type: "View", parentNativeID: (N/A), index: 0, nativeID: (N/A)}',
+    'Delete {type: "View", nativeID: (N/A)}',
+    'Create {type: "View", nativeID: (N/A)}',
+    'Insert {type: "View", parentNativeID: (N/A), index: 0, nativeID: "child"}',
+    'Insert {type: "View", parentNativeID: (N/A), index: 0, nativeID: (N/A)}',
+  ]);
+});

packages/react-native/ReactCommon/react/renderer/mounting/Differentiator.cpp

@@ -736,8 +736,6 @@ static void calculateShadowViewMutationsFlattener(
           // Flatten parent, unflatten child
           else {
             // Unflatten old list into new tree
-            // TODO(T217775046): Find a test case for this branch of view
-            // flattening + culling.
             auto parentTagForUpdateWhenFlattened =
                 ReactNativeFeatureFlags::
                     enableFixForParentTagDuringReparenting()
@@ -759,8 +757,8 @@ static void calculateShadowViewMutationsFlattener(
                      : parentTag),
                 /* parentSubVisitedOtherNewNodes */ subVisitedNewMap,
                 /* parentSubVisitedOtherOldNodes */ subVisitedOldMap,
-                /* oldCullingContext */ adjustedOldCullingContext,
-                /* newCullingContext */ adjustedNewCullingContext);
+                oldCullingContext,
+                newCullingContext);
 
             // If old nodes were not visited, we know that we can delete them
             // now. They will be removed from the hierarchy by the outermost